1. Field of the Invention
The present invention relates generally to a method for removing contaminants from dredge material. More specifically, the present invention relates to a method which uses a reactor vessel to generate a slurry vortex to treat contaminated sediments in an underwater environment.
2. Description of the Prior Art
At present, technologies and processes for managing contaminated dredge material in an under water environment require elaborate contaminant separation, handling, treatment and disposal facilities and processes. Innovative dredge heads have been designed during the last decade in an attempt to mitigate the environmental impact of dredging in conjunction with site specific processes and operations for the removal of contaminants from the ocean floor and monitoring procedures for determining the level of contamination.
Nevertheless, physical removal of contaminated sediments by conventional dredging processes invariably results in contaminant losses and off site migration due to the generation of sediment plumes and desorption of contaminants when exposed to oxidizing lacustrine or sea water. Following removal, highly contaminated dredged material can be classified as hazardous waste, requiring physical separation from xe2x80x9cclean spoilsxe2x80x9d, or non-contaminated sand and soils, special handling, ex situ treatment and/or expensive disposal in land based hazardous waste sites. The disposal of highly contaminated dredged material can be very costly, i.e., up to one thousand dollars per cubic yard. There is also the additional problem of filling land fills with contaminated sediments since these land fills generally have limited available space for hazardous waste disposal.
In many cases, severe contaminated sediments are derived from a single pollutant source, such as a shore-based industrial facility which has dumped contaminants into a nearby stream or river or directly into the lake or ocean. In these cases the contamination is often concentrated in xe2x80x9chot spotsxe2x80x9d in close proximity to their source.
Accordingly, there is a need to provide for a method or process which allows for in situ cleanup of highly contaminated sediment reducing xe2x80x9chot spotxe2x80x9d sediment contaminant levels.
Reducing xe2x80x9chot spotxe2x80x9d sediment contaminant levels allows for the leaving of cleaned sediments in their place, or for the removal and disposal by conventional dredging methods with minimal environmental risk.
The present invention overcomes some of the difficulties of the past including those mentioned above in that it comprises a relatively simple yet highly effective method which uses a reactor vessel for in situ cleanup of severe sediment contamination in an underwater environment.
The method of the present invention comprises the steps of
(1) positioning a reactor vessel above a contaminated area on the ocean floor which has a contaminated sediment material;
(2) penetrating the contaminated area on the ocean floor with the reactor vessel by removing seawater from within the reactor vessel to create a negative pressure within the reactor vessel;
(3) introducing a pressurized fluid into the reactor vessel to create a slurry vortex of the contaminated sediment material;
(4) injecting a remediation fluid into the slurry vortex of the contaminated sediment material using a sufficient amount of the remediation fluid to remediate the contaminated sediment material and provide a noncontaminated sediment material; and
(5) injecting pressurized seawater into the interior of the reactor vessel to create a positive pressure within the reactor vessel to lift the reactor vessel above the ocean floor allowing for a transfer of the reactor vessel to another area of sediment contamination on the ocean floor.